Table I.

Quantification of Fluorescent Signals

				A6 cells		Embryonic nuclei
FISH		5′ETS		75 ± 8		335 ± 60
FISH		rRNAs		1,180 ± 300		331 ± 60
Ratio				1/15		1/1
FISH		5′ETS		75 ± 8		335 ± 60
run-on		elongating transcripts		483 ± 100		no nucleolar signal  (expected 2,167)
Ratio				1/6.5		—

FISH is less sensitive than run-on assays to detect unprocessed transcripts. Quantification of fluorescence signals was performed with NIH image 1.56 on acquisitions obtained after FISH with rDNA and 5′ETS probes and run-on assays on A6 cells or embryonic nuclei 9 h after fertilization. For each method, 20 images were chosen at random and the same thresholding was applied. The signal was quantified leading to an integrated density value. The mean of 20 values is given for each case and the ratios between the different methods are established (Ratio).